Re: [C++ PATCH] Diagnose constexpr overflow (PR c++/70323)

[Jason Merrill]

On 03/23/2016 02:34 PM, Jason Merrill wrote:

For GCC 7 we should do constexpr evaluation on the unfolded function,
but for GCC 6 this is OK.

And here's a fix for the -Wall case.

Tested x86_64-pc-linux-gnu, applying to trunk.



commit 75f153ad9c455c7f2340b6da6791e5a9a0787a8e
Author: Jason Merrill <ja...@redhat.com>
Date:   Thu Mar 24 12:53:32 2016 -0400

    	PR c++/70323
    	* constexpr.c (cxx_eval_call_expression): Don't cache result if
    	*overflow_p.

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 8427513..2d30a84 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -1448,7 +1448,7 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
 
       if (result == error_mark_node)
 	*non_constant_p = true;
-      if (*non_constant_p)
+      if (*non_constant_p || *overflow_p)
 	result = error_mark_node;
       else if (!result)
 	result = void_node;
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-70323a.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-70323a.C
new file mode 100644
index 0000000..d166787
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-70323a.C
@@ -0,0 +1,11 @@
+// PR c++/70323
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wall" }
+
+constexpr int overflow_if_0 (int i) { return __INT_MAX__ + !i; }
+constexpr int overflow_if_1 (int i) { return __INT_MAX__ + i; }
+
+constexpr bool i0_0 = overflow_if_0 (0);   // { dg-error "overflow in constant expression" }
+constexpr bool i0_1 = overflow_if_0 (1);
+constexpr bool i1_0 = overflow_if_1 (0);
+constexpr bool i1_1 = overflow_if_1 (1);   // { dg-error "overflow in constant expression" }